In the manufacture of optical fiber, an optical glass preform is suspended vertically and moved so that successive increments of length are moved into a furnace. As a result of the temperature within the furnace, optical fiber is able to be drawn from the leading end of the preform.
After the fiber is drawn from the preform, the fiber is provided with one or more layers of coating material. Typically, the coating material is an ultraviolet light energy curable material. Consequently, after the coating material has been applied, the coating material is cured. Subsequently, the coated, drawn fiber is measured and taken up on a spool.
Typically, the curing apparatus includes an elliptical reflector or housing having a curing lamp which extends longitudinally parallel to the path of the fiber. The lamp or bulb as it frequently is called is positioned at one of the focal points of the elliptical reflector. The bulb emits radiation toward a longitudinally extending center tube, the center of which is positioned at the focal point of another portion of the elliptical housing aligned with the portion of the housing in which the bulb is positioned. The drawn optical fiber is advanced through the center tube and radiation from the bulb passes through the center tube to engage the fiber and cure the coating material. Radiation which scatters to the interior surface of the elliptical housing is reflected back into engagement with the fiber which is being moved along a path coincident with the loci of the focal points of successive sections of the reflector.
A blanket of an inert gas is caused to become disposed about the coated, drawn fiber as it is advanced through the center tube. This is done in order to facilitate surface curing of the coating materials. Otherwise, any oxygen which is present inhibits the curing of the coating material.
As the curing process proceeds, the optical fiber off-gases and clouds the tube. With the passage of time, the amount of radiation which reaches the fiber is reduced until a point is reached when substantially only a portion of the radiation gets through to the fiber. Accordingly, it becomes necessary periodically to change the center tube in order to maintain a consistent cure level.
Presently, the elliptical housing, the center tube and the bulb are disposed in the hinged enclosure having openings at the top and bottom thereof. When it comes time to replace a center tube, the center tube is moved in a longitudinal direction slidably upwardly or downwardly out of the enclosure and a replacement center tube moved into its place.
The existing center tube replacement process presents some practical problems. The optical fiber drawing line is oriented so that the fiber path is vertical and the preform is suspended vertically. Not only does the drawing line include a furnace, apparatus for the application of coating materials and curing apparatus, but also it includes apparatus for performing various measurements on the drawn and on the coated fiber. As a result, space on the line is at a premium. In order to gain access to the center tube, the enclosure is moved partially so that a production technician can extend hands into the enclosure and move the center tube longitudinally vertically. In order to remove a center tube by movement longitudinally vertically, an additional length of space must be provided above or below the curing apparatus or the curing apparatus must be dismantled substantially. This of course detracts from space available for other processes, given that there is a limited amount of space between a floor and a ceiling which can be occupied by a draw tower.
Also, the bulbs need to be cooled during operation, typically with a high flow rate of air. Exhaust ducts are attached to the enclosure and lead to fans which pull out the air. These are aligned vertically in sections and associated with each section is an exhaust duct system. In the past, these exhaust ducts have had to be removed from the enclosure prior to the pivotal movement of the enclosure and the removal of the interior center tube.
Of course, any solution to these problems must be mindful of the present arrangement of elements of the curing apparatus. It is usual that a set of magnetrons be disposed adjacent to an associated bulb and that the bulb, the center tube and the drawn optical fiber be aligned.
What is desired and seemingly what is not available in the prior art of curing apparatus for optical fiber coating material is an enclosure, which enclosure facilitates replacement of a center tube without the need for additional space above or below the enclosure or without the severe dismantling of the curing apparatus. The sought-after enclosure must be such that it does not interfere with the present alignment of elements of the curing apparatus and desirably is such that the exhaust system need not be disassembled from the curing apparatus prior to replacement of the center tube.